1. Field of the Invention
The present invention relates to a method for producing an aldehyde or a ketone, which is useful in the field of organic synthetic chemistry, through an oxidation reaction of an alcohol under a mild condition, along with easy removal of a byproduct.
2. Description of the Related Art
Extensive investigations have been hitherto conducted on the reactions of oxidizing a primary alcohol into an aldehyde, and oxidizing a secondary alcohol into a ketone, in view of the usefulness of aldehydes and ketones in the field of organic synthesis. Among these oxidation reactions, Pfitzner-Moffatt oxidation by which an oxidation reaction of an alcohol is carried out using dicyclohexylcarbodiimide (hereinafter, abbreviated to “DCC”), dimethyl sulfoxide (hereinafter, abbreviated to “DMSO”) and an acid, has been reported as one of effective oxidation reactions that can be carried out under mild reaction conditions of room temperature and near neutrality, without using a highly toxic heavy metal oxidizing agent or an explosive oxidizing agent (K. E. Pfitzner and J. G. Moffatt, J. Am. Chem. Soc., 85, 3027 (1963)).
However, in this reaction, since dicyclohexylurea generated from DCC after the reaction exhibits some dissolubility in those solvents generally used in oxidation reactions, such as DMSO, benzene and toluene, there is a need for a method of precipitating such a urea compound by exchanging the solvent with a solvent having low dissolvability for the urea compound after the reaction, and removing the resulting precipitate through filtration. Furthermore, this method requires complicated operations, and it is difficult to completely separate the urea compound that is produced as a byproduct (Lectures on Experimental Chemistry, 4th Edition, Vol. 21, 1.1 “Oxidation from Alcohol, a. DMSO-DCC Method”, p. 11-13, published by Maruzen Co., Ltd.).
Meanwhile, there have been reports on the methods which can be used to facilitate the separation of these urea compounds that are produced as byproducts from carbodiimide compounds. One method is reported to involve the use of a water-soluble carbodiimide such as 1-ethyl-3-(3-N,N-dimethylaminopropyl)-carbodiimide (hereinafter, abbreviated to “EPCI”) or hydrochloride thereof, so that the urea compound that is produced as a byproduct after the reaction can be removed by extraction with water (J. C. Sheehan, P. A. Cruickshank, and G. L. Boshart, J. Org. Chem. Soc., 26, 2525 (1961) and Japanese Patent Application Unexamined Publication No. 6-116216).
Furthermore, another method has been reported, which is a method of introducing a carbodiimide group into the aromatic ring of polystyrene that has been crosslinked with divinylbenzene, such as an N-alkylcarbodiimide polystyrene resin, to make the resin insoluble in the reaction solvent, so that the urea compound produced as a byproduct after the reaction can be removed by filtration (for example, N-cyclohexylcarbodiimide polystyrene resin, manufactured by Tokyo Chemical Industry Co., Ltd.) (Organic Synthesis, Vol. 56, 99 (1977)).